Purpose: In treatment planning of charged-particle radiotherapy, patient heterogeneity is conventionally modeled as variable-density water converted from CT images to best reproduce the stopping power, which may lead to inaccuracies in the handling of multiple scattering and nuclear interactions. Although similar conversions can be defined for these individual interactions, they would be valid only for specific CT systems and would require additional tasks for clinical application. This study aims to improve the practicality of the interaction-specific heterogeneity correction. Methods: We calculated the electron densities and effective densities for stopping power, multiple scattering, and nuclear interactions of protons and ions, using the standard elemental-composition data for body tissues to construct the invariant conversion functions. We also simulated a proton beam in a lung-like geometry and a carbon-ion beam in a prostate-like geometry to demonstrate the procedure and the effects of the interaction-specific heterogeneity correction. Results: Strong correlations were observed between the electron density and the respective effective densities, with which we formulated polyline conversion functions. Their effects amounted to 10% differences in multiple-scattering angle and nuclear-interaction mean free path for bones compared to those in the conventional heterogeneity correction. Although their realistic effect on patient dose distributions would be generally small, it could be at the level of a few percent when a carbon-ion beam traverses a large bone. Conclusions: The present conversion functions are invariant and may be incorporated in treatment planning systems with a common function relating CT number to electron density. This will enable improved beam dose calculation while minimizing initial setup and quality management of the user's specific system.
We carried out experiments to investigate the light output response of NaI(Tl), CsI(Tl), GSO(Ce) and LYSO(Ce) crystals for intermediate-energy 4 He, 12 C and 40 Ar beams from HIMAC at National Institute of Radiological Sciences. And we investigate the light output of these crystals for several-energy gamma-ray for comparison. From these light output responses, we obtained the relationships between the scintillation efficiency (dL/dx) and the specific energy loss (dE/dx) for each crystal. The scintillation efficiency curves of NaI(Tl) and CsI(Tl) crystal have the peak in a particular dE/dx. On the other hand, the scintillation efficiency curves of GSO(Ce) and LYSO(Ce) crystal decrease with increasing dE/dx. The light output curves of these crystals were systematically reproduced using obtained scintillation efficiencies.
Breast cancer is increasingly being detected at earlier stages, and partial breast irradiation for patients with low-risk-group tumor has come to be applied in the US and Europe as an alternative to whole-breast irradiation. Based on those experiences, some institutes have tried using particle beams for partial breast irradiation for postoperative or radical intent for early breast cancer, but technical difficulties have hindered its progress. The National Institute of Radiological Sciences has been preparing for carbon-ion radiotherapy (C-ion RT) with radical intent for stage I breast cancer since 2011, and we carried out the first treatment in April 2013. In this case report, we explain our first experience of C-ion RT as a treatment procedure for breast tumor and present the radiation techniques and preliminary treatment results as a reference for other institutes trying to perform the same kind of treatment.
For carbon-ion beams, POM was dosimetrically indistinguishable from water and the best of the plastics examined in this study. The poorest was HDPE, which would reduce the Bragg peak by 0.45% per cm range shift, although with marginal superiority for reduced multiple scattering. Between the two clear plastics, PET would be superior to PMMA in dosimetric water equivalence.
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